Fume incinerators heretofore have been used for eliminating combustible fumes from the off gases of various industrial processes. In one type of fume incinerator utilized for this purpose, commonly referred to as a thermal oxidizer, the process gas stream is oxygen bearing and serves as the source of oxygen for combusting an auxiliary fuel to establish a flame in which the combustible fumes are incinerated. Typically, the process gas stream is first preheated by being passed in heat exchange relationship with the combustion products of the thermal oxidizer as the process gas stream is being passed to the burner or burners of the thermal oxidizer. By preheating the process gas stream prior to combustion, the overall efficiency of the combustion process is increased and the amount of fuel consumed in the combustion of the process gas stream is reduced.
The fume-laden gases given off by some industrial processes contain volatile organic compounds (VOC's) and other organic constituents that tend to build up on the surfaces of the heat exchanger through which the fume-laden gases are passed before being passed to the burner or burners of the thermal oxidizer. This build-up progressively reduces the efficiency of the heat exchanger. Moreover, the heat exchanger passages may become clogged to a point that significantly restricts the flow of fume-laden gases. In the past this problem was solved by periodically removing the build-up from the heat exchanger passages. This not only was a tedious and time consuming task, but the thermal oxidizer necessarily had to be taken out of service to permit such cleaning operation. Unless a redundant thermal oxidizer was provided, shut down of the thermal oxidizer would normally necessitate shut down of the entire processing line, with obvious negative economic consequences.